48,610 research outputs found
SamACO: variable sampling ant colony optimization algorithm for continuous optimization
An ant colony optimization (ACO) algorithm offers
algorithmic techniques for optimization by simulating the foraging behavior of a group of ants to perform incremental solution
constructions and to realize a pheromone laying-and-following
mechanism. Although ACO is first designed for solving discrete
(combinatorial) optimization problems, the ACO procedure is
also applicable to continuous optimization. This paper presents
a new way of extending ACO to solving continuous optimization
problems by focusing on continuous variable sampling as a key
to transforming ACO from discrete optimization to continuous
optimization. The proposed SamACO algorithm consists of three
major steps, i.e., the generation of candidate variable values for
selection, the ants’ solution construction, and the pheromone
update process. The distinct characteristics of SamACO are the
cooperation of a novel sampling method for discretizing the
continuous search space and an efficient incremental solution
construction method based on the sampled values. The performance
of SamACO is tested using continuous numerical functions
with unimodal and multimodal features. Compared with some
state-of-the-art algorithms, including traditional ant-based algorithms
and representative computational intelligence algorithms
for continuous optimization, the performance of SamACO is seen
competitive and promising
Colossal infrared and terahertz magneto-optical activity in a two-dimensional Dirac material
When two-dimensional electron gases (2DEGs) are exposed to magnetic field,
they resonantly absorb electromagnetic radiation via electronic transitions
between Landau levels (LLs). In 2DEGs with a Dirac spectrum, such as graphene,
theory predicts an exceptionally high infrared magneto-absorption, even at zero
doping. However, the measured LL magneto-optical effects in graphene have been
much weaker than expected because of imperfections in the samples available so
far for such experiments. Here we measure magneto-transmission and Faraday
rotation in high-mobility encapsulated monolayer graphene using a custom
designed setup for magneto-infrared microspectroscopy. Our results show a
strongly enhanced magneto-optical activity in the infrared and terahertz ranges
characterized by a maximum allowed (50%) absorption of light, a 100% magnetic
circular dichroism as well as a record high Faraday rotation. Considering that
sizeable effects have been already observed at routinely achievable magnetic
fields, our findings demonstrate a new potential of magnetic tuning in 2D Dirac
materials for long-wavelength optoelectronics and plasmonics.Comment: 14 pages, 4 figure
Towards Quantitative Classification of Folded Proteins in Terms of Elementary Functions
A comparative classification scheme provides a good basis for several
approaches to understand proteins, including prediction of relations between
their structure and biological function. But it remains a challenge to combine
a classification scheme that describes a protein starting from its well
organized secondary structures and often involves direct human involvement,
with an atomary level Physics based approach where a protein is fundamentally
nothing more than an ensemble of mutually interacting carbon, hydrogen, oxygen
and nitrogen atoms. In order to bridge these two complementary approaches to
proteins, conceptually novel tools need to be introduced. Here we explain how
the geometrical shape of entire folded proteins can be described analytically
in terms of a single explicit elementary function that is familiar from
nonlinear physical systems where it is known as the kink-soliton. Our approach
enables the conversion of hierarchical structural information into a
quantitative form that allows for a folded protein to be characterized in terms
of a small number of global parameters that are in principle computable from
atomary level considerations. As an example we describe in detail how the
native fold of the myoglobin 1M6C emerges from a combination of kink-solitons
with a very high atomary level accuracy. We also verify that our approach
describes longer loops and loops connecting -helices with
-strands, with same overall accuracy.Comment: 3 figure
Mode-locking of incommensurate phase by quantum zero point energy in the Frenkel-Kontorova model
In this paper, it is shown that a configuration modulated system described by
the Frenkel-Kontorova model can be locked at an incommensurate phase when the
quantum zero point energy is taken into account. It is also found that the
specific heat for an incommensurate phase shows different parameter-dependence
in sliding phase and pinning phase. These findings provide a possible way for
experimentalists to verify the phase transition by breaking of analyticity.Comment: 6 pages in Europhys style, 3 eps figure
Alternative proof for the localization of Sinai's walk
We give an alternative proof of the localization of Sinai's random walk in
random environment under weaker hypothesis than the ones used by Sinai.
Moreover we give estimates that are stronger than the one of Sinai on the
localization neighborhood and on the probability for the random walk to stay
inside this neighborhood
Immunization for complex network based on the effective degree of vertex
The basic idea of many effective immunization strategies is first to rank the
importance of vertices according to the degrees of vertices and then remove the
vertices from highest importance to lowest until the network becomes
disconnected. Here we define the effective degrees of vertex, i.e., the number
of its connections linking to un-immunized nodes in current network during the
immunization procedure, to rank the importance of vertex, and modify these
strategies by using the effective degrees of vertices. Simulations on both the
scale-free network models with various degree correlations and two real
networks have revealed that the immunization strategies based on the effective
degrees are often more effective than those based on the degrees in the initial
network.Comment: 16 pages, 5 figure
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